The goal of this research is to enhance our ability to utilize menstrual cycle diaries and menstrual histories as epidemiologic tools in the investigation of risk factors for reproductive dysfunction and of hormonally-mediated risk factors for chronic disease. Two basic problems will be addressed: 1) How to define consistent, biologically meaningful menstrual cycle endpoints for use in epidemiologic research; and 2) How to analyze menstrual diary data. The natural variability in menstrual cycle patterns within women across the reproductive lifespan will be characterized. Change in cycle length from cycle to cycle within women will be quantified and age-specific changes in the population distribution of cycle length and cycle variability will also be evaluated. A strategy for analyzing menstrual diary data will be developed by applying existing statistical methods for longitudinal data. New statistical methodology will also be developed. Efficient study protocols to obtain data on menstrual cycle patterns among low-income and minority women across the reproductive life span will then be designed, as currently available US data is generally limited to white, college-educated women. The primary source will be lifetime menstrual records for 942 women from the Tremin Trust, a unique prospective study of menstrual cycle patterns which utilized menstrual diaries. Daily urinary hormone data for nonconception cycles from a prospective study of early pregnancy loss will also be examined. This proposal is designed to redress fundamental gaps in knowledge about menstrual cycle characteristics over the life course and to provide substantive data to guide the design and direction of future epidemiologic research.